1. Field of the Invention
The present invention relates to a moulding material (hereinafter referred to as the impression material) used for the preparation of the oral tissue models required for the preparation of dental prostheses such as crowns, inlays or dentures and, more especially, to a dental precise impression material comprising silicone, which is designed to be used for precise impression material.
2. Statement of the Prior Art
Dental impression materials are generally broken down into non-elastic and elastic types.
The non-elastic impression materials may include those formed of wax, gypsum, modelling compounds and the like. With the non-elastic impression materials, however, it is hardly possible to achieve any precise moulding (impression) of the teeth, arrangement of the teeth, jaw and mucosa, each having a complicated shape and form and including undercuts, of the oral cavity, since they undergo no elastic deformation. Because of this, general moulding (impression) of the oral cavity is presently carried out with modelling compounds to form an individual tray, which is merely used in combined impression with other precise impression materials.
The elastic impresstion materials may include those formed of agar, alginates, polysulfide rubber, polyether rubber, silicone rubber and the like. The elastic impression materials make it possible to take the impressions of the teeth, arrangement of the teeth, jaw and mucosa, each having a complicated shape and form and including undercuts, of the oral cavity, since they are elastically deformable so that, when removing the impression from within the oral cavity, their deformation, if any, is restorable to the original form.
While the agar or alginate impression materials are advantageous in that they show a suitable degree of elasticity from the clinical point-of-view, and are easy to handle and relatively inexpensive, they are disadvantageous in that they undergo a considerable extent of permanent deformation, and that the impression obtained therefrom and taken out of the oral cavity changes largely in dimensions with the lapse of time due to their large amount of moisture content and tends to be readily torn due to their low tear strength. For those reasons, they are mainly used for snap impression.
The synthetic rubber-based impression materials obtained by using a raw material e.g., polysulfide rubber, polyether rubber and silicone rubber are used for precise impression, since they show a suitable degree of elasticity from the clinical point-of-view, are easy to handle and give rise to fairly small permanent deformation, and provide cured products which show only limited dimensional changes with the lapse of time and high tear strength.
Of the types of synthetic rubber forming the impression materials, the polysulfide rubber is disdvantageous in that it gives out strong offensive odor, and is cured too slowly; and the polyether rubber is of reduced elasticity and hard, and is largely affected by moisture. However, the silicone rubber is most frequency used as the impression material, because it provides a material which is tasteless and odorless, is sharply cured, excels in elasticity and exhibits excellent dimensional stability owing to its extremely limited dimensional change.
Depending upon the curing manner involved, the silicone rubber is classified into the condensation type and the addition type. Such room temperature-vulcanization silicone rubber is utilized as the dental silicone impression material. In general, one of the condensation type silicone impression material is available on one hand in the form comprising a base component consisting of a hydroxydimethyl polysiloxane having hydroxide groups at its both terminals and a catalyst component consisting of an alkyl orthosilicate and an organic tin compound which, in use, are mixed and kneaded together by an operator (typically a dentist) to prepare a mixture, which is then subjected to condensation vulcanization and setting at normal temperature to provide elastic silicone rubber, whereas the other is available in the form comprising a base component consisting of a hydroxydimethyl polysiloxane having hydroxide groups at its both terminals, a crosslinker (reactor) component consisting of alkyl orthosilicate and a catalyst component consisting of an organic tin compoubnd which, in use, are mixed and kneaded together by an operator to obtain a mixture, which is then subjected to condensation vulcanization and setting at normal temperature to provide elastic silicone rubber.
On the other hand, the addition type impression materials are generally available in the form comprising a base component consisting of a hydrogen polymethylsiloxane and a catalyst component consisting of a vinyl polymethylsiloxane having a vinyl group and a platinum catalyst added thereto, which, in use, are mixed and kneaded together by an operator to obtain a mixture, which is then subjected to addition vulcanization and setting at normal temperature to provide elastic silicone rubber.
The silicone impression materials based on such silicone rubber have the following excellent features:
1. They are readily mixable and kneadable. PA1 2. They are sharply set in the oral cavity. PA1 3. They excel in elastic recovery. PA1 4. The surface of a gypsum model is smooth. PA1 5. They provide a set body which undergoes only limited dimensional changes and, hence, excels in dimensional stability. PA1 6. They are tasteless and odorless. PA1 (A) ether types wherein the number of addition moles of ethylene oxide or propylene oxide is 1 to 30, and an alkyl group has 12 to 22 carbon atoms, such as polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether and polyoxyethylene alkyl phenyl ether, PA1 (B) partial ester types of polyhydric alcohols and fatty acids having 12 to 22 carbon atoms, such as sorbitan.fatty acid esters, glycerin.fatty acids esters, polyglycerin.fatty acid esters, ethylene glycol.fatty acid esters, polyethylene glycol.fatty acid esters, propylene glycol.fatty acid esters and pentaerythritol.fatty acid esters, PA1 (C) ether ester types wherein the number of addition moles of ethylene oxide is 1 to 30, and a fatty acid has 12 to 22 carbon atoms, such as polyoxyethylene sorbitan.fatty acid esters, polyoxyethylene sorbitol.fatty acid esters, polyoxyethylene mannitan.fatty acid esters, polyoxyethylene glyceryl fatty acid esters, and polyoxyethylene propylene glycol.mono-fatty acid esters, and PA1 (D) ester types of ethylene oxide obtained by addition polymerization, wherein the number of addition moles of ethylene oxide is 1 to 30, such as polyoxethylene castor oil.hardened castor oil, polyoxyethylene lanolin derivatives, polyoxyethylene phitosterol and polyolxyethylene beeswax derivatives. PA1 Rf is a fluorinated aliphatic or aromatic group having 1 to 20 carbon atoms provided that the aliphatic group may be straight, branched or cyclic, PA1 B is a divalent connecting group (e.g., --SO.sub.2 -- and --CO), PA1 R' is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and PA1 l, m and n each are an integer of 1 to 50. PA1 (a) Hydroxydimethyl polysiloxanes having hydroxide groups at its both terminals. PA1 (b) Crosslinkers, typically, ortho- or poly-ethyl silicates having an ethoxy group PA1 (c) Condensation vulcanization catalysts, typically, organometallic compounds such as dibutyltin acetate, dibutyltin laurate and lead octenoic acid. PA1 (d) Fillers, typically, diatomaceous earth, calcium carbonate, silicic acid, calcium sulfate, zirconium silicate, zirconium oxide, titanium oxide and zinc oxide. Alternatively, fillers surface-treated with resins, silane or the like. PA1 (e) If necessary, coloring matters, perfumes, fluidity regulators, plasticizers and the like. PA1 (1) Vinylpolymethyl siloxanes having a vinyl-terminated group. PA1 (2) Hydrogen polymethyl siloxanes having an active hydrogen-terminated group. PA1 (3) Addition vulcanization catalysts, typically, platinum base catalysts. PA1 (4) Fillers, typically, diatomaceous earth, calcium carbonate silicic acid, calcium sulfate, zirconium silicate, zirconium oxide, titanium oxide and zinc oxide. Alternatively, fillers surface-treated with resins, silane or the like. PA1 (5) If necessary, coloring matters, perfumes, fluidity regulators, plasticizers and the like.
Thus, the best use is now made of the silicone impression materials.
With the silicone impression materials, however, it is difficult to take the precise impressions of the details of the oral cavity and, hence, reproduce precisely the details of the oral cavity on a gypsum model, when the oral cavity is wetted with blood, saliva or other fluids. This is because the silicone rubber possesses water repellency as one of its properties.
More specifically, when the oral cavity is wetted with saliva blood, or other fluids at the time of taking the impression of the oral cavity, the blood, saliva or other fluids are forced into the details such as interdentiums, margins of the teeth or pits and fissures in the teeth by the silicone impression material, and are allowed to remain there, since the silicone impression material shows unsatisfactory compatibility with respect to blood, saliva or other fluids. There is now a tendency that impression is carried out in that state, which renders it difficult to take detailed and precise impressions. At the time of impression, it is thus required for an operator to blow air to the regions of the oral cavity, the impressions of which are to be taken, followed by sufficient drying. This operation is troublesome for not only an operator but also a patient, and is especially difficult to apply to an infant or bleeding regions. At the time of the preparation of a gypsum model, there is a tendency that gypsum slurry is repelled on the registered surface of the impression taken, thus rendering it hard to cast it into the details of the registered surface and bringing about easy entrainment of air bubbles therein, since that surface shows unsatisfactory compatibility with respect to the gypsum slurry. It is thus difficult to precisely transfer the details of the registered surface onto the gypsum model. For that reason, it is required for an operator to cast the gypsum slurry into the details of the registered surface, while applying it thereonto in small portions by means of a brush. This operation needs careful attention, and is very troublesome for an operator. In order to solve the above-mentioned problems arising from the unsatisfactory wettability and compatibility which the silicone impression material show with respect to saliva, blood or other fluids or gypsum slurry, the addition of nonionic surface active agents to the silicone impression materials has hitherto been considered.
However, large amounts of such nonionic surfactants have had to be added to the silicone impression materials for the purpose of eliminating the wettability and compatibility problems. As a result, other problems arise, such as deteriorations of the physical properties due to inhibited setting reaction of silicone rubber and surface roughening of the gypsum model.